Aircraft electrical distribution systems have become increasingly complex. The complexity, in part, is a by-product of the fact that most multi-engine aircraft have generators associated with each engine. The generators are driven through integrated drive trains which provide a constant speed output to the generators even though the engines are operating at varying speeds. The electrical wiring is strung throughout the wings and fuselage of the aircraft which results in a number of regions within the aircraft where an electrical wiring fault may occur. While broadly speaking, a fault may be an open circuit condition; the faults to which the invention is directed are of the short circuit type. The presence of a fault of the short circuit type, if not instantly detected and isolated from a power generating source, results in heightened probability of an electrically caused fire at the fault. It is not uncommon for modern aircraft to have in addition to the generators driven by the aircraft engines an additional or auxiliary engine that drives an auxiliary power generator. The main generators driven from the aircraft's engines as well as the auxiliary power generator are mutually interconnected via a distribution bus and circuit breakers to thereby provide a plurality of power channels or paths to the aircraft electrical system loads. The detection of faults within the electrical distribution system and the control of breakers to isolate faults and redirect power has been a concern for many years. The detection of faults through the employment of inductively coupled differential current detection circuits has been utilized as is evidenced by Flugstad U.S. Pat. No. 2,974,257. Flugstad provides a protective apparatus for a power system in which the distribution network is fed from parallel connected generators. FIG. 1 of Flugstad illustrates the presence of a pair of generators 12 and 14, which have direct current field windings 16 and 18, respectively, and neutral armature conductors 20, 22, 24 and 26, 28, 30, respectively. Feeder bus networks 32 and 34 are arranged to be connected to a paralleling bus network 64. Generator circuit breakers 48 and 50 respectively connect generator output conductors 52, 54, 56 and 58, 60, 62 to conductors 36, 38, 40 and 42, 44, 46. Bus tie breakers 72 and 74 connect these last noted conductors to the parallel bus 64. Differential fault detection is provided by sensing circuits 194 and 196. The sensing circuits 194 and 196 control the energization of direct current field windings 16 and 18 of generators 12 and 14 as well as bus tie breakers 72 and 74. Flugstad offers no system for clearing faults throughout an entire distribution system. Flugstad also does not contemplate the provision of fault detection when many loads are fed through a number of power channels from a plurality of power sources.
The Deter U.S. Pat. No. 3,617,812 is directed to differential fault detection for providing short circuit protection for electrical networks such as those found in airborne power supply systems. The Deter system includes a series of current transformers 10, 11, 15, 16, 17 for monitoring the input leads C.sub.1, C.sub.2 and output leads C.sub.3, C.sub.4, C.sub.5 of a network and further provides a summing circuit 20 for summing the output signals from the current transformers 10, 11, 15, 16, 17. Where a fault exists in the network, a nonzero current summation will result and a corresponding output is fed to a comparator 30 and thence to a control unit 40 which initiates a programmed switching operation within the network to locate the fault. It can be seen that Deter requires a multitude of switch operations with attendant time delays in order to locate a fault. Deter does not provide, as applicant's invention will demonstrate, an ability to immediately locate a fault and clear the fault while leaving as many loads fully powered as possible. The invention to be described accomplishes the clearing of faults with a minimum of breaker action all of which cannot be duplicated by either Flugstad or Deter.